Process and fabrication methods for emitter wrap through back contact solar cells

Abstract

Back contact solar cells including rear surface structures and methods for making same. The rear surface is doped to form an n + emitter and then coated with a dielectric layer. Small regions are scribed in the rear surface and p-type contacts are then formed in the regions. Large conductive grid areas overlay the dielectric layer. The methods provide for increasing efficiency by minimizing p-type contact areas and maximizing n-type doped regions on the rear surface of a p-type substrate.

1 . A method for making a back-contact solar cell, the method comprising the steps of: 
 providing a semiconductor substrate comprising a first conductivity type;    providing a diffusion comprising an opposite conductivity type on the rear surface;    depositing a dielectric layer on the rear surface;    forming a plurality of holes extending from a front surface of the substrate to a rear surface of the substrate;    removing the diffusion and dielectric layer from one or more regions of the rear surface;    creating one or more contacts comprising the first conductivity type in each of the one or more regions;    disposing a first conductive grid on the rear surface in electrical contact with the contacts; and    disposing a second conductive grid on the rear surface in electrical contact with the diffusion in the holes.    
     
     
         2 . The method of  claim 1  wherein the creating step comprises doping the substrate with a dopant.  
     
     
         3 . The method of  claim 2  wherein the dopant comprises an element selected from the group consisting of boron and aluminum.  
     
     
         4 . The method of  claim 2  wherein the first conductive grid does not comprise the dopant.  
     
     
         5 . The method of  claim 1  wherein the step of providing a diffusion comprises exposing the substrate to a gas.  
     
     
         6 . The method of  claim 5  wherein the gas comprises POCl 3 .  
     
     
         7 . The method of  claim 1  wherein the first conductive grid is interdigitated with the second conductive grid.  
     
     
         8 . The method of  claim 1  wherein the depositing step comprises depositing the dielectric layer on the front surface and the creating step comprises simultaneously providing a second diffusion comprising an opposite conductivity type on the interior surfaces of the holes.  
     
     
         9 . The method of  claim 1  further comprising the step of constructing a passivation layer on one or both of the front surface and the rear surface.  
     
     
         10 . The method of  claim 9  wherein the constructing step comprises a method selected from the group consisting of oxidizing the surface or depositing the passivation layer on the surface.  
     
     
         11 . The method of  claim 1  further comprising the step of coating the interior surfaces of the holes and the one or more region with a plated metallic contact layer, wherein the coating step is performed after the creating step and prior to the disposing steps.  
     
     
         12 . The method of  claim 11  wherein the contact layer comprises nickel.  
     
     
         13 . The method of  claim 11  wherein the contact layer is plated using electroless plating.  
     
     
         14 . The method of  claim 11  further comprising the step of providing a second diffusion after the removing step, the second diffusion comprising an opposite conductivity type on the interior surfaces of the holes and the one or more regions; wherein the creating step comprises overdoping the second diffusion.  
     
     
         15 . A back contact solar cell made according to the method of  claim 1 .  
     
     
         16 . A back contact solar cell comprising a plated layer comprising a metal, said layer disposed between one or more doped regions of the substrate and one ore more conductive grids, wherein said conductive grids do not comprise the metal.  
     
     
         17 . The back contact solar cell of  claim 16  wherein said metal comprises nickel.  
     
     
         18 . A method for making a back-contact solar cell, the method comprising the steps of: 
 providing a semiconductor substrate comprising a first conductivity type;    depositing a patterned dielectric layer on the rear surface;    providing a diffusion comprising an opposite conductivity type on open portions of the rear surface not covered by the dielectric layer;    disposing a metal on the open portions and on the dielectric layer adjacent to the open portions; and    firing the metal.    
     
     
         19 . The method of  claim 18  wherein the depositing step comprises screen printing the dielectric layer.  
     
     
         20 . The method of  claim 18  wherein the step of providing a diffusion comprises using a gas selected from the group consisting of POCl 3  and PH 3 .  
     
     
         21 . The method of  claim 18  wherein the metal comprises a dopant of the first conductivity type.  
     
     
         22 . The method of  claim 21  wherein the disposing step comprises screen printing a paste comprising the metal.  
     
     
         23 . The method of  claim 18  wherein the firing step comprises spiking the diffusion in the open portions with the metal.  
     
     
         24 . A back-contact solar cell made according to the method of  claim 18.